1. Field of the Invention
This invention relates to an apparatus for contacting with a flowing gas two mutually opposite, substantially flat and substantially circular annular surfaces of annular cylindrical workpiece having an inside diameter not in excess of a predetermined maximum inside diameter, which apparatus comprises an oven housing, which contains two mutually opposite plenum chambers, which are defined by respective side walls, which are spaced apart in an axial direction and define between them an oven chamber adapted to accommodate said workpiece in a position in which each of said side walls faces one of said surfaces of said workpiece, each of said side walls being formed with orifice slot means, and means for supplying a gas to said plenum chambers. In particular the invention relates to an apparatus for contacting with a flowing gas two mutually opposite, substantially flat and substantially circular annular end faces of an annular cylindrical workpiece consisting of a strip coil, which is provided with a tubular core having an outside diameter which defines the inside diameter of said strip coil.
2. Description of the Prior Art
In such apparatuses the flowing gas is usually employed to transfer heat to a workpiece, particularly to a strip coil, and it is desired to ensure a uniform supply of the flowing gas to the substantially flat surfaces of the workpiece so that a uniform heat transfer and optionally also a uniform mass transfer between the flowing gas and the surfaces of the workpiece is ensured because otherwise the workpiece may not be uniformly heated and the surface of the strip coil may exhibit a non-uniform color change. Said risks will be particularly high if a high heat transfer rate is desired in order to shorten the annealing time.
U.S. Pat. No. 4,736,529 discloses an apparatus which has on each side a plurality of orifice slots, which extend radially at least approximately in a plane and through which gas streams are discharged in a direction which is inclined relative to the side wall which is formed with said slots and defines a plenum chamber so that the gas is uniformly supplied to the surfaces of the workpiece. But it has been found that the desired result is not satisfactorily produced because only a very small part of the heat content of the gas which is discharged through the radially outer end portions of the orifices is transferred to the workpiece and said gas is mixed with gas which has transferred heat to the end face of the coil or to the surface of another workpiece but can still compensate the heat losses of the gas which is discharged near the periphery of the coil or other workpiece so that the coil or other workpiece is heated to higher temperature in regions of its peripheral surface.